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Characterization of Minerals Carriers Fluorine and Chlorine Associated with Copper Ore

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Characterization of Minerals Carriers Fluorine and Chlorine Associated with Copper Ore XXVI Encontro Nacional de Tratamento de Minérios e Metalurgia Extrativa Poços de Caldas-MG, 18 a 22 de Outubro 2015 CHARACTERIZATION OF MINERALS CARRIERS FLUORINE AND CHLORINE ASSOCIATED WITH COPPER ORE FREITAS, M.E., GRAVINA, E.G.1, PEREIRA, A.C.2, MACHADO, G.A.A.2, TEODORO, M.A.M.2 1,2CIT SENAI FIEMG, ISI em Processamento Mineral, e-mail: [email protected] ABSTRACT The chemical composition reflects the formation requirements of a mineral deposit. When combined with the detailed study of rock mineralogy and their textural relationships, it may provide a basis for understanding the form of occurrence of a contaminant element and guide the mineral processing requirements. Often, the high F- content is attributed to the presence of fluorite. However, when the amount of this mineral is incipient, other minerals become important due to its high concentration in the rock. Copper mineralization host rocks are characterized by the existence of a great variety of minerals, and by the superposition of deformation and alteration events, thus leading to complex textural relationships. The most abundant copper sulphides are considered of secondary formation and occur preferentially in amphibole and biotite cleavages and fractures, which are carriers of F-, or as micro inclusions in later alteration minerals. The occurrence of mixed particles in the flotation concentrate portrays the intergrowth relations of minerals in the rocks. Data from mineral chemistry show that F- content decreases in the alteration minerals of biotite and amphibole, which are the main carriers of this element. Cl-, on the other hand, has its contents preserved, or augmented with the evolution of the alteration. KEYWORDS: Cu-sulfides; biotite; amphibole; bearing minerals F- and Cl-. RESUMO A composição química reflete as condições de formação de um depósito mineral, que combinada ao estudo detalhado da mineralogia e da petrografia, pode proporcionar a compreensão da forma de ocorrência de um elemento contaminante e servir de guia para o processamento mineral. Muitas vezes, o alto teor de F-, contaminante em minério de Cu, está associado à fluorita. No entanto, quando a quantidade desse mineral é incipiente, outros se tornam importantes devido à sua alta concentração. Rochas mineralizadas em Cu são caracterizadas pela variabilidade mineralógica e pela superposição dos eventos de deformação e alteração, conduzindo a relações texturais complexas. Nos minérios estudados, os sulfetos de Cu mais abundantes são considerados de formação secundária e ocorrem preferencialmente em clivagens e fraturas de anfibólio e biotita, que são portadores de F-, ou como microinclusões em minerais de alterações posteriores. A ocorrência de partículas mistas nos concentrados da flotação retrata as relações de intercrescimento dos minerais nas rochas. Os dados de química mineral demonstram que o conteúdo de F- diminui nos minerais de alteração de biotita e anfibólio. Cl-, por outro lado, tem o seu conteúdo preservado, ou aumentado com a evolução da alteração. PALAVRAS-CHAVE: Cu-sulfetos; biotita; anfibólio; minerais portadores de F- e Cl-. Freitas, M.E.; Gravina, E.G.; Pereira, A.C.; Machado, G.A.A.; Teodoro, M.A.M. 1. INTRODUCTION The mineralogical variety of mineral deposits is linked to the formation and alteration conditions, and in order to enable an economic concentration of the ore, several stages of change and / or deformation are needed. The interaction of magmatic granitic fluids with mafic host rocks in hydrothermal systems, resulting in the geochemical bimodal character and the presence of an impermeable rock contributes to the fluid conduit. Thus, in some deposits, such as copper related to granites and mafic rocks reactive, there are noted sulfides with very different levels of sulfur in regions of relative geographical proximity. The cupric-gold deposit considered in this work is located in the Serra de Carajás, Brazil. It´s a rare mineralization model (Choque Fernandez et al., 2005) consisting of significantly deformed and hydrothermalized rocks (andesitics basalts and dacites), in which the original mineralogy was completely replaced. The Cu mineralization occurs as sulphide ores and oxidized ore. The sulphide ore occurs in disseminated forms (predominant), massive sulphide and filling fractures. The host rocks are biotite-magnetite schists, with amphibole (grunerite-cummingtonite and hastingsite subordinates), fayalite and garnet. The mineralized portions consist mainly of bornite, chalcopyrite and chalcocite (subject) as well as varying proportions of molybdenite, covellite, cobaltite, saflorite, niquelite, siegenite, Au, Ag, graphite, ilmenite, hematite, Te-Ag, uraninite and rare earths minerals. Amphibole, garnet, quartz and plagioclase may occur in varying proportions, and along other silicates, form 40% of the rocks. Fluorite, greenalite, minnesotaite, stilpnomelane, apatite, monazite, allanite, siderite, goethite and malachite occur in smaller quantities (Choque Fernandez, 2002). The high content of F- in rock and ore can be explained by the strong influence of granite signature in the area. The presence of late fluorite indicates the importance of fluids rich in F- and Cl- during hydrothermal alteration (Teixeira et al., 2010; Pollard, 2000). The F- and Cl- ions can replace the OH- in various hydrated silicates, such as mica and amphibole. The presence of F- in garnet is less common, but can occur in special formation conditions (Manning & Bird, 1990; Valey et al., 1983; Gunow et al., 1980). The presence of these ions in clay minerals is also dependent on the composition of the original mineral and on the stability of mineral phases. 2. MATERIALS AND METHODS In the samples studied were performed granulochemical studies, mineral chemistry and mineralogical characterization in order to identify and understand the behavior of the F- and Cl- bearing minerals in the copper ore. As the main objective research was the minerals carriers F- and Cl- remaining in the cooper ore flotation concentrate, the study was focused on samples of feeding, concentrate and tailing. Additional studies were performed in ROM samples to the knowledge of the mineralization host rock and the relationship of the possible F- bearing minerals with mineral ore. In this sense, granulochemical studies have not been conducted in these samples. XXVI Encontro Nacional de Tratamento de Minérios e Metalurgia Extrativa Poços de Caldas-MG, 18 a 22 de Outubro 2015 The flotation samples were dried at 90°C and sent for particle size analysis by sieving (mesh opening between 75 and 38 µm) and ciclosyzer (in fractions -75 and - 38 µm). Different size fractions were sent for chemical analysis of whole rock by ICP- AES and ICP-MS. The F was analyzed by specific ion, and the Cl by colorimetry. Mineralogical analyzes were performed by optical microscopy on polished thin sections and X-ray diffraction. The procedure involved an optical microscope coupled with imaging system, Leica DMLP and diffractometer Shimadzu XRD 6000, with CuKα radiation (λ = 1,5418Å), 0.02 pitch and speed 0.50o/min, from 4° to 80° 2θ. For the interpretation of diffraction the Match! 2 software (Putz, 2003-2015) was applied. Microchemistry analyzes were performed on an electron microprobe JEOL, JXA- 8900R model with four spectrometers WDS-eight crystals. The following standards were used: F (fluorite), Fe (magnetite), Cl (Cl apatite), Na (jadeite), Ba (barium sulfate synthetic), K (sanidine), Si (quartz), Mn (Mn hortonolite), Mg (Mg hortonolite), Ti (rutile), Al (Al2O3), Zn (synthetic ZnO), Ca (synthetic CaF2). Calibration conditions were: 15kV, 20ŋA, with times of 30s to F, Cl for 20s and 10s for the other elements. 3. RESULTS AND DISCUSSION 3.1. Granulochemical analysis Based on the results of the whole rock chemical analysis of different size fractions of feeding, concentrate and flotation tailings, the grade distributions of SiO2, Al2O3, K2O, Fe2O3, MgO, Na2O, F and Cu were performed. These oxides were chosen because they represent the major constituents of silicates, such as mica and amphibole, which in turn are the potential carriers of F- that is the target of these studies, while copper is the primary constituent of the ore. The Cl- in the chemical analysis of the whole rock appeared below the detection limit in all samples. The flotation feed has 29% of particles larger than 75 µm, while 48% below 38 µm, 35% of which is silt. The distribution of SiO2 and Al2O3 appears with a trend pattern: about 33% in the thicker fraction (+75 µm), decreased levels in the intermediate, and increased up to 44% of the finer one (-38 µm). K2O, MgO and Na2O have the same tendency of these two species, but the coarsest fraction reaches 38%, which may be indicative of a higher concentration of mica. Fe2O3 appears mainly in the finer fraction. The same was observed for the distribution of F- and Cu. The flotation concentrate may be classified as superfine: 86% is below 38 µm. The distribution of oxides shows that more than 83% of the content of SiO2, Al2O3, K2O, - Fe2O3 and Cu are found in fractions below 38 µm. In the case of F , MgO and Na2O, 72% are below 38 µm, and 37% are in the fraction below 14.7 µm. The flotation tailings are characterized by 42% of superfine material (-38 µm) with about 43% of the material above 30.5 µm. A clear correlation of the distribution of SiO2, Al2O3, K2O, MgO and Na2O can be observed in fractions +75 µm and -38 µm: 38-48% and 33-44%, respectively. The finest fraction (-38 µm) is richest in the contents of F-, Fe, about 48%, and Cu with 55%. Freitas, M.E.; Gravina, E.G.; Pereira, A.C.; Machado, G.A.A.; Teodoro, M.A.M. 3.2. Mineralogical identification Mineralogical studies by optical microscopy in rock fragments of ROM were instrumental in helping to identify the mineralogy of feed, concentrate and flotation tailings samples, due to the very fine grain size (40-86% of the material below 38 µm), and to the predominance of mixed particles.
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